This application claims the priority of German application 196 49 402.8 filed in Germany on Nov. 28, 1996, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a pressure control system of vehicles having intake and exhaust valves actuated by solenoids for the controlled venting and bleeding of the brake system consuming devices.
In electropneumatic brake systems, actuators of many different types are used for controlling the brake pressure. The actuators in these systems must carry out the service brake function as well as the ABS-function. In this case, it is necessary to permit slow smooth pressure changes for the service brake function as well as rapid pressure changes for the emergency brake or the ABS function. Either valves are used which can carry out both functions, or different valves are used separately for each function. Among others, proportional solenoid valves with and without a relay valve, with and without ABS pressure control valves; also double solenoid valves for the pilot control of a relay valve, with and without ABS pressure control valves are used as well as current-controlled pilot control solenoid valves with seat valves, the latter for both functions.
In an attempt to develop smooth adjustments of the consuming device pressure, pressure control devices have been developed in the case of which, while the consuming device pressure is monitored on the consuming device side by a pressure sensor, intake and exhaust valves are provided which interact with pilot valves in such a manner that, in the course of the electric drive of solenoid valves actuating the intake and exhaust valves, in a manner which is limited with respect to time, a throttled opening of the pilot control valves is permitted. As the excitation of the actuating magnets increases, the pilot control valves are shut and the actual main valves are opened up over a large cross-section. In the case of these types of control devices, the desired smooth feeding of the consuming device pressure is determined by a plurality of parameters. In addition, intermediate and floating positions of the main valves exist which must be defined as a function of the exciting current. The constructional expenditures of such pressure control deices are therefore considerable. In addition, functional precision is required under different temperature and pressure conditions.
Based on the above, it is an object of the invention to further develop a pressure control device of the above-mentioned type by simple means in such a manner that it can carry out service brake functions as well as ABS functions and, in particular, it is suitable for providing smooth pressure changes during service braking as well as rapid pressure changes when required by emergency braking or ABS functions. As the result of the structure of such pressure control devices, the use of pilot control units should also not be necessary.
This object is achieved according to preferred embodiments of the invention by providing a pressure control device for electropneumatic brake systems of the type referred to above, wherein the intake valve connected between a compressed air supply and a consuming device and/or an exhaust valve connected between the consuming device and a pressure relief (atmosphere) is provided with an intake cross-section or exhaust cross-section which can be changed by way of the piston stroke of its valve piston, and wherein a pressure medium chamber of a pressure control device, which is fed by the intake valve and is connected with the consuming device, is continuously monitored by a pressure sensor with respect to the controlled-in pressure or the pressure to be reduced, which pressure sensor transmits the determined pressure values to an electronic control unit for actuating the solenoid of the intake valve or exhaust valve.
Because of the sensor-dependent drive of the solenoids of the intake valve and the exhaust valve and because of the precisely defined contouring of the valve pistons of the intake valve and the exhaust valve at their approach-flow-side end, it is possible as a function of the stroke to achieve any targeted pressure change and volume change for the consuming device. That is, because of the stroke-dependent change of the available cross-section between the intake end of the valve piston and the inside cross-section of the housing directly receiving the valve piston, it is possible to adapt the course of the pressure to the respective braking situation. The air flow can therefore be proportioned in a targeted manner by way of a flow cross-section which can be changed by way of the piston stroke of the intake valve and/or the exhaust valve. As a result, it becomes possible that:
(i) during an emergency braking, the whole cross-section and therefore a rapid pressure rise can be obtained; PA1 (ii) in the case of an ABS-control, the large cross-sections can also be used; PA1 (iii) in the case of smooth braking operations and slow changes, small flow cross-sections and therefore slow pressure changes are permitted; PA1 (iv) the dynamic course of the braking signal, for example, a rapid pressure rise to approximately 90% of the brake pressure and then a slower pressure rise, can be implemented merely by the change of the flow cross-section; and PA1 (v) the so-called wheel module of the brake system learns the pressure gradient for the venting and bleeding because the volumes connected behind consisting of the brake hose and the brake cylinder remain constant after the installation so that, corresponding to the level and mainly the time dependency of the braking signal, an optimal controlling is permitted.
As far as the constructional criteria of such a pressure control device are concerned, important advantages can also be achieved; that is, the service brake function as well as the ABS function can be implemented by means of one module. Furthermore, the air consumption is that of the present brake systems; that is, there is no increased air consumption as a result of timing valves. Also, no noises have to be accepted, as they disadvantageously occur in the case of timed valves or pulsating valves. It is also an advantage that the device operates essentially independently of the temperature because of its current control.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.